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Rasmus Andreasen

Early earth and solar system evolution - Insights from strontium, barium neodymium, and samarium isotopes

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Recent thermal ionization mass spectrometer advances have made it possible to determine the isotopic composition of both terrestrial and extra-terrestrial samples with unrivaled precision. The coupled long- and short-lived samarium- neodymium decay system ( 147 Sm[arrow right] 143 Nd, t ? =106 Ga, 146 Sm[arrow right] 142 Nd, t ? =103 Ma) have been used to confirm the presence of 142 Nd variations in early Archean samples, and to show that the depleted upper mantle is elevated in 142 Nd compared to chondrite meteorites. These results imply that major silicate differentiation of the Earth's mantle occurred within about 30 Ma after accretion. Furthermore, they require the presence of an enriched reservoir that has not interacted with the depleted mantle since initial differentiation. This study presents high-precision thermal ionization mass spectrometer data for strontium, barium, neodymium, and samarium isotopic compositions of meteorite and terrestrial samples in order to investigate: (i) whether the 142 Nd differences between meteorites and terrestrial samples are indeed caused by the decay of 146 Sm with variable Sm/Nd ratios, (ii) if their Nd isotopic compositions are fundamentally different due to variations in nucleosynthetic components or neutron fluences; and (iii) if traces of the early enriched reservoir can be found in deep mantle plume derived lavas carrying solar noble gas signatures. The Sm, Nd, and Ba isotopic compositions of carbonaceous chondrites are found to be different from that of ordinary chondrites, the eucrite parent body, and Earth, which are all identical. Non-radiogenic Sr isotopic compositions are identical for terrestrial samples and meteorites. Variations in nucleosynthetic components (s-, r-, and p-process) within the Solar System are evident from p- process deficits in Sm and Nd and r-process excesses in Ba for carbonaceous chondrites. The p-process deficit explains the bimodal 142 Nd distribution seen in chondrites but is insufficient to explain the difference between chondrites and the terrestrial upper mantle. No signs of the early enriched reservoir were found in deep mantle plume lavas from the Iceland hot spot and Deccan Flood basalts. However, this could be due to dilution with depleted upper mantle material. Combined, these results point to a homogenous inner Solar System with respect to heavy elements and confirm early terrestrial mantle differentiation.
TidsskriftProquest Dissertations And Theses 2007. Section 0059, Part 0372 160 pages; [Ph.D. dissertation].United States -- New Hampshire: Dartmouth College; 2007. Publication Number: AAT 3290539. Source: DAI-B 68/12, Jun 2008
StatusUdgivet - 1 aug. 2007
Eksternt udgivetJa

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